Flux modifier for a permanent magnet brush-type motor using wound field coils combined with permanent magnets

ABSTRACT

A stator and armature assembly  12  is provided for a permanent magnet DC motor. The assembly includes an armature  13  having a lamination core  14  and windings  15,  and a stator structure  16  associated with the armature. The armature is constructed and arranged to rotate with respect to the stator structure. The stator structure includes at least one permanent magnet  22  providing a certain flux, and at least one wound core structure  17  having a core  18  and a coil  19  wound about the core so as to define an alternate pole with respect to the permanent magnet. When current to the coil is controlled, flux of the stator structure  16  can be increased or decreased relative to the certain flux. In this way a motor can operate at different speeds.

This application is based on U.S. Provisional Application No.60/529,191, filed on Dec. 12, 2003 and claims the benefit thereof forpriority purposes.

FIELD OF THE INVENTION

The invention relates to permanent magnet brush-type DC motors and, moreparticularly, to wound field coils combined with permanent magnets in astator structure.

BACKGROUND OF THE INVENTION

A significant challenge of permanent magnet DC brush-type motors is toachieve different speeds of operation. Wound Field type motors generallyhave speed controlled by altering the field flux. This is done bychanging the current or the number of coil turns of the field winding.Since permanent magnet motors have a constant field flux, they cannotachieve speed control by field flux variation.

Often, permanent magnet motors used in automotive applications requirethe use of more than one speed, usually a lower speed for generalpurpose operation and a maximum speed for worst case operation. Forexample, multiple speed operation of a vehicle cooling system moduleprovides a more optimized engine temperature and operation, whichconsequently contributes to improved fuel economy.

For permanent magnet DC brush-type motors, historically lower speeds(multiple speed operation) have been achieved by the following methods:

-   -   Adding a resistor in series with the motor    -   Switching out brushes (lap wind motor)    -   Dual armature winding with dual commutator    -   Adding an additional 3^(rd) brush (short out coils)    -   External or internal electronic control comprised of but not        limited to:    -   SSR, (Solid State Relays)    -   Linear Control    -   PWM, (Pulse Width Modulation)

FIGS. 1A, 1B and 1C show a magnetic circuit of 2 pole, 4 pole and 6 poleconventional brush-type permanent magnet DC motor, respectively. Thelines of flux are created such that they leave the North Pole magnet andenter into the air gap. The flux lines enter into a lamination stack ofa rotor of the motor and travel along the shortest possible path to themagnet of opposite polarity. The lines of flux again travel through theair gap and into the magnet of opposite polarity. The lines of flux thenleave the second magnet and return back to the original magnet. Hence,the lines of flux are understood to operate in a closed loop circuit.The flux available in the air gap between the magnet and the rotorlamination determines the operating characteristics of the motor.

The magnetic flux can be produced using either a wound field stator orpermanent magnet stator. FIG. 2 shows the magnetic circuit of a 2 polewound field motor where the (N) coils of wire around a pole shoe 10produce the magnetic flux. One concern is that motors with permanentmagnets have a constant level of field flux (or stator flux) and henceonly operate with one speed. The advantage of a wound field stator isthat various windings can be applied to change the level of field fluxor stator flux. The disadvantage of using a wound field stator is thatin order to generate sufficient field flux, significant numbers of coilturns are required for each field coil. This requirement causes thestator to be bulky, heavy and relatively expensive.

In examination of conventional speed control methods another method tovary the motor flux is to combine permanent magnets with field woundcoils to produce the desired level of flux.

SUMMARY OF THE INVENTION

An object of the invention is to fulfill the need referred to above. Inaccordance with the principles of the present invention, this objectiveis achieved by providing a stator and armature assembly for a permanentmagnet DC motor. The assembly includes an armature having a laminationcore and windings, and a stator structure associated with the armature.The armature is constructed and arranged to rotate with respect to thestator structure. The stator structure includes at least one permanentmagnet providing a certain flux, and at least one wound core structurehaving a core and a coil wound about the core so as to define analternate pole with respect to the permanent magnet. When current to thecoil is controlled, flux of the stator structure can be increased ordecreased relative to the stator flux. In this way a motor can operateat different speeds.

In accordance with another aspect of the invention, a method ofcontrolling speed of a permanent magnet DC motor is provided. The motorincludes an armature having a lamination core and windings; and a statorstructure associated with the armature. The armature is constructed andarranged to rotate with respect to the stator structure. The statorstructure includes at least two permanent magnets of the same polaritythat provide a certain flux; and at least two wound core structures ofthe same polarity. Each wound core structure has a core and a coil woundabout the core. The wound core structures define alternate poles withrespect to the permanent magnets. The method provides switchesoperatively associated with the motor and coils. The switches arecontrolled so that 1) no current is provided to the coils so that thearmature rotates at a certain speed based on the certain flux of thepermanent magnets, 2) current is provided to the coils in one directionso that flux increases relative to the certain flux, causing thearmature to rotate, for example, at a speed less than the certain speedor 3) current is provided to the coils in a direction opposite the onedirection so that flux decreases relative to the certain flux, causingthe armature to rotate, for example, at a speed greater than the certainspeed.

Other objects, features and characteristics of the present invention, aswell as the methods of operation and the functions of the relatedelements of the structure, the combination of parts and economics ofmanufacture will become more apparent upon consideration of thefollowing detailed description and appended claims with reference to theaccompanying drawings, all of which form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings, wherein like reference numerals refer tolike parts, in which:

FIG. 1A shows a magnetic circuit for a conventional 2 pole brush-typepermanent magnet motor.

FIG. 1B shows a magnetic circuit for a conventional 4 pole brush-typepermanent magnet motor.

FIG. 1C shows a magnetic circuit for a conventional 6 pole brush-typepermanent magnet motor.

FIG. 2 shows a magnetic circuit of a conventional 2 pole wound fieldmotor.

FIG. 3 is a plan view of 4 pole stator and armature assembly inaccordance with the principles of the present invention.

FIG. 4 is a plan view of a wound core structure of the stator andarmature assembly of FIG. 3.

FIG. 5 is a perspective view of a ferrous core, of the wound corestructure of FIG. 4, shown without wire coil.

FIG. 6 is a graph of motor operation characteristics of a motor of theinvention.

FIG. 7 is a schematic illustration showing coils of a motor of theinvention being connected in parallel.

FIG. 8 is a schematic illustration showing coils of a motor of theinvention being connected in series.

FIG. 9 is a table showing a three speed switching operation of a motorof FIGS. 7 and 8.

FIG. 10 is a schematic illustration showing a coil switching arrangementof a motor according to another embodiment of the invention.

FIG. 11 is a table of seven-speed switching operation for the circuit ofFIG. 10.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 3 shows a 4 pole stator and armature assembly, generally indicatedat 12, provided in accordance with the principles of the invention for afour pole permanent magnet DC brush-type motor 11 (shown schematicallyin FIG. 7). The assembly 12 includes a conventional armature, generallyindicated at 13, having a lamination core 14 and windings 15, and astator structure, generally indicated at 16, surrounding the armature13. The armature 13 is constructed and arranged to rotate with respectto the stator structure when the windings 15 are energized. The motor 11can be of the type disclosed in U.S. Pat. No. 5,977,666, the contents ofwhich is hereby incorporated into the present specification byreference. The motor 11 is preferably used in automotive applicationssuch as, for example, engine cooling applications. Although a 4 poleassembly is shown, it can be appreciated that the invention isapplicable to 2, 6, 8, . . . etc. pole motors.

In FIG. 3, in the stator structure 16, alternate pole pieces are woundcore structures, generally indicated at 17. A wound core structure 17 isshown in FIG. 4 and includes a ferrous core 18 and a winding or coil 19wound about the core 18. As shown in FIG. 5, the core 18 includes a base20 and a bobbin member 21 extending from the base 20. The bobbin member21 and base 20 are constructed and arranged to define a pocket 25 forreceiving a portion of the coil 19. The bobbin member 21 has aperipheral surface 23 upon which the coil 19 is wound. The surface 23can be coated with epoxy or other substances to provide electricalinsulation between the coil 19 and core 18.

As shown in FIG. 3, the stator structure 16 main flux is supplied by thetwo permanent magnets 22 and 24 having the same polarity. The adjacentpoles (cores) 18 are made from a ferrous material similar in geometricsize to a permanent magnet 22 or 24. The two ferrous cores 18 are eachconfigured so that a coil 19 of wire is wound to about the core 18 andenergizing the coil 19 provides extra field flux to the assembly 12.This additional flux created by the coils 19 is used to enhance orreduce the main field flux created by the permanent magnets 22 and 24.

The two coils 19 are wound similarly to a wound field motor. The coils19 are each wound with “N” turns of “X” gauge wire and are wound in thesame direction and are of the same polarity when coils are energized.The polarity of the wound cores is determined by the direction of thewire winding in coils 19 and the direction of current flowing throughthe coils 19. The coils 19 are wound either in a Clockwise (CW) orCounter-Clockwise (CCW). The coils 19 are installed around the ferritecore 18 at alternate positions relative to the permanent magnets 22 and24.

The motor and permanent magnet circuits are configured so that themotor's magnetic field is significantly below the magnetic saturationpoint for the closed loop magnetic circuits. This will likely be thecase since the number of permanent magnets has been reduced by half ascompared to a conventional permanent magnet motor. Hence, each magneticcircuit (Pole) is only supported by one permanent magnet and not by two,as in a conventional permanent magnet motor. This results in a loweroperating point for the magnet (due to a lower slope on the magnet loadline, Pc Line).

When there is no flux intervention from the stator coils 19, the motor11 operates at a certain speed (Medium Speed). The motor operationcharacteristics are illustrated in FIG. 6. The flux level can beincreased by adding extra flux generated by the field coils 19. Theadditional flux slows the motor 11, thus defining a Low Speed when fluxis added to the motor. The field coils 19 are used to diminish the fluxfrom the permanent magnet motor 11 by energizing the coils 19 in theopposite direction. The effect of this is to increase the operatingspeed of the motor (High Speed).

Therefore, three different operating speeds (Medium, Low and High) canbe accomplished. A switching scheme for three-speed operation istabulated in FIG. 9, with K1-K3 being power switches, such as, forexample, electromagnetic relays or MOSFETs. Furthermore, the coils 19can be connected electrically in parallel to each other (FIG. 7) or inseries (FIG. 8). FIGS. 7 and 8 show electrical connection between avehicle electrical system 30 and an engine cooling module 32 of avehicle. In FIGS. 7 and 8, CON is the power connection to the fieldwound coils 19, M+ is motor Positive Connection, and M− is motorNegative Connection. FIG. 6 shows a graph of motor operationcharacteristics of a motor of the invention. In FIGS. 7 and 8, the coilsare not energized. The K1, K2, and K3 switches are in “OFF” position.The motor flux is due to magnets only.

Additional speed variation can be achieved by selectively energizing(switching) coils 19 independently from each other or together incombination in series and parallel connection. An example of thisswitching method is tabulated in FIG. 11 and illustrated schematicallyin FIG. 10. In this case the coils are not energized. The K1, K2 . . .K6 switches are in “OFF” position. The motor flux is due to magnetsonly. Note that up to seven different speeds can be achieved byselectively controlling current to the coils 19. K1-K6 are powerswitches, such as, for example, electromagnetic relays or MOSFETs. InFIG. 10, the switches are considered to be part of the motor, but can beseparate therefrom.

It can be appreciated that the core 18 can be a separate part that isassembled to the stator structure housing and thereafter wound.Alternatively, the separate core 18 can be wound and then mounted to thestator structure housing. Another option is to create the core integralwith the wall of the stator structure housing and then wind the coilthereabout.

Thus, permanent magnets are combined with field wound coils to producethe overall flux level of the stator structure 16. Furthermore the basicmotor 11 has a fixed flux level due to the two permanent magnets 22, 24and the two field-wound coils 19. When the coils are energized they canadd to or cancel out the flux in the stator structure 16. The fluxchange in the motor will provide a variable operating speed.

Advantages of the stator structure 16 include:

-   -   1. The motor speed is controlled by the field coils 19.    -   2. The motor main flux is produced by the permanent magnets 22        and 24.    -   3. The current levels in the field coils 19 are low and this        allows the use of smaller relays.    -   4. Good motor efficiency at low speed.    -   5. Vehicle relay system can be used to control power to wound        field coils.

Other features of the stator structure 16 include:

-   -   1. Combination of wound field coils 19 and permanent magnets to        achieve motor action.    -   2. Changing motor speed by replacing “n” magnets with “n” wound        field coils 19 and switching coils 19 ON, OFF, and Reverse-ON.    -   3. Use of single coils connected with power switch        (Relay/MOSFET) in series or parallel to achieve change in flux        or motor speed.    -   4. Use of pre-connected field wound coils with power switches        (Relay/MOSFET) in series or parallel to achieve change in flux        or motor speed.    -   5. Coils being independent components or integral part of        housing component/assembly.    -   6. Power switches can be part of the motor assembly or built        into an external box, or part of the car Engine Computer Unit,        or part of the vehicle electrical system.    -   7. Voltage of at least one coil 19 can be detected to measure        armature speed change for use in stall protection at the same        time or independently. Alternatively, an additional winding can        be added to sense armature speed.

The foregoing preferred embodiments have been shown and described forthe purposes of illustrating the structural and functional principles ofthe present invention, as well as illustrating the methods of employingthe preferred embodiments and are subject to change without departingfrom such principles. Therefore, this invention includes allmodifications encompassed within the spirit of the following claims.

1. A stator and armature assembly for a permanent magnet DC motor,comprising: an armature having a lamination core and windings, and astator structure associated with the armature, the armature beingconstructed and arranged to rotate with respect to the stator structure,the stator structure comprising: at least one permanent magnet providinga certain flux, and at least one wound core structure having a core anda coil wound about the core so as to define an alternate pole withrespect to the permanent magnet such that controlling current to thecoil increases or decreases flux in the stator structure relative to thecertain flux.
 2. The assembly of claim 1, wherein the core is of ferrousmaterial and has a peripheral surface about which the coil is wound. 3.The assembly of claim 1, wherein the core is of generally the samegeometric size as the permanent magnet.
 4. The assembly of claim 1,wherein the core includes a base and a bobbin member extending from thebase, the bobbin member and base being constructed and arranged todefine a pocket for receiving a portion of the coil.
 5. The assembly ofclaim 4, wherein the bobbin member has a peripheral surface about whichthe coil is wound.
 6. The assembly of claim 5, wherein the surface iselectrically insulated.
 7. The assembly of claim 1, wherein the statorstructure has a housing, the core being separate from the housing andmounted thereto.
 8. The assembly of claim 1, wherein the statorstructure has a housing, the core being integral with the housing.
 9. Astator structure for a permanent magnet DC motor, the stator structurecomprising: at least one permanent magnet providing a certain flux, andat least one wound core structure having a core and a coil wound aboutthe core so as to define an alternate pole with respect to the permanentmagnet such that controlling current to the coil increases or decreasesflux in the stator structure relative to the certain flux.
 10. Thestructure of claim 9, wherein the core is of ferrous material and has aperipheral surface about which the coil is wound.
 11. The structure ofclaim 9, wherein the core is of generally the same geometric size as thepermanent magnet.
 12. The structure of claim 11, wherein the statorstructure has a housing, the core being separate from the housing andmounted thereto.
 13. The structure of claim 11, wherein the statorstructure has a housing, the core being integral with the housing.
 14. Astator structure for a permanent magnet DC motor, the stator structurecomprising: at least two permanent magnets of the same polarity andproviding a certain flux, and at least two wound core structures of thesame polarity, each wound core structure having a core and a coil woundabout the core, the wound core structures defining alternate poles withrespect to the permanent magnets such that controlling current to thecoils increases or decreases flux in the stator structure relative tothe certain flux.
 15. The structure of claim 14, wherein each core is offerrous material and has a peripheral surface about which the coil iswound.
 16. The structure of claim 14, wherein each core is of generallythe same geometric size as each permanent magnet.
 17. The structure ofclaim 14, in combination with an armature, the armature having alamination core and windings, and being constructed and arranged torotate with respect to the stator structure.
 18. The structure of claim14, wherein the stator structure has a housing, the core being separatefrom the housing and mounted thereto.
 19. The assembly of claim 14,wherein the stator structure has a housing, the core being integral withthe housing.
 20. A permanent magnet DC motor, the motor including:armature having a lamination core and windings, and a stator structureassociated with the armature, the armature being constructed andarranged to rotate with respect to the stator structure, the statorstructure comprising: at least two permanent magnets of the samepolarity and providing a certain flux, and at least two wound corestructures of the same polarity, each wound core structure having a coreand a coil wound about the core, the wound core structures definingalternate poles with respect to the permanent magnets such thatcontrolling current to the coils increases or decreases flux in thestator structure relative to the certain flux.
 21. The motor of claim20, wherein the coils are connected electrically in parallel.
 22. Themotor of claim 20, wherein the coils are connected electrically inseries.
 23. The motor of claim 20, in combination with switchesconstructed and arranged with respect to the motor and coils to beselectively controlled to control current to the coils and thereby fluxin the stator structure to rotate the armature and thus the motor atdifferent speeds.
 24. The combination of claim 20, wherein the switchesare constructed and arranged such that when 1) no current is provided tothe coils, the armature rotates at a certain speed, 2) current isprovided to certain of the coils in one direction, flux increasescausing the armature to rotate at a speed less than the certain speedand 3) current is provided to certain of the coils in a directionopposite the one direction, flux decreases causing the armature torotate at a speed greater than the certain speed.
 25. The combination ofclaim 23, wherein the switches are separate from the motor.
 26. Thecombination of claim 23, wherein the switches are integral with themotor.
 27. The motor of claim 20, wherein the stator structure has ahousing, the core being separate from the housing and mounted thereto.28. The motor of claim 20, wherein the stator structure has a housing,the core being integral with the housing.
 29. A method of controllingspeed of a permanent magnet DC motor, the motor including an armaturehaving a lamination core and windings; and a stator structure associatedwith the armature, the armature being constructed and arranged to rotatewith respect to the stator structure, the stator structure including atleast two permanent magnets of the same polarity that provide a certainflux; and at least two wound core structures of the same polarity, eachwound core structure having a core and a coil wound about the core, thewound core structures defining alternate poles with respect to thepermanent magnets, the method including: providing switches operativelyassociated with the motor and coils, and controlling the switches to sothat 1) no current is provided to the coils so that the armature rotatesat a certain speed based on the certain flux of the permanent magnets,2) current is provided to certain of the the coils in one direction sothat flux increases relative to the certain flux, causing the armatureto rotate at a speed less than the certain speed or 3) current isprovided to certain of the coils in a direction opposite the onedirection so that flux decreases relative to the certain flux, causingthe armature to rotate at a speed greater than the certain speed. 30.The method of claim 29, further including: detecting a voltage of atleast one of the coils to measure speed of the armature for use indetermining a stall condition.